rustdoc: remove redundant item kind class from `.item-decl > pre`

This class originated in the very first commit of `rustdoc_ng`, and was used
to add a color border around the item decl based on its kind.

https://github.com/rust-lang/rust/blob/4fd061c426902b0904c65e64a3780b21f9ab3afb/src/rustdoc_ng/html/static/main.css#L102-L106

The item decl no longer has a border, and there aren't any
kind-specific styles in modern rustdoc's rendering of this UI item.

Most of this commit is updating test cases so that they use `item-decl` to
find the `<pre>` tag instead of relying on the fact that the class name
had `rust {kind}` in it while other `<pre>` tags only had class `rust`.

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/rustdoc/const-generics/generic_const_exprs.rs b/tests/rustdoc/const-generics/generic_const_exprs.rs
index 215ee228eb8..c53cf6dcd05 100644
--- a/tests/rustdoc/const-generics/generic_const_exprs.rs
+++ b/tests/rustdoc/const-generics/generic_const_exprs.rs
@@ -2,6 +2,6 @@
 #![feature(generic_const_exprs)]
 #![allow(incomplete_features)]
 // make sure that `ConstEvaluatable` predicates dont cause rustdoc to ICE #77647
-// @has foo/struct.Ice.html '//pre[@class="rust struct"]' \
+// @has foo/struct.Ice.html '//div[@class="item-decl"]/pre[@class="rust"]' \
 //      'pub struct Ice<const N: usize>;'
 pub struct Ice<const N: usize> where [(); N + 1]:;